Engine/Transmission (1994 - 1998) new 12 valve

[dray]

I'm the new owner of a 12v cummins w/ 120,000 miles. I have been reading this forum for a week and joined TDR yesterday. Though I want to bomb this truck later, I would like to modify it so that it gets the best gas mileage now. When my trans gives up the ghost, I will upgrade to a hipo model and bomb away. What would be the route to go for best mileage? Exhaust, air filter, syn oil..... ? I am confused a little by all the talk on exhaust. Should I go cat back, remove cat and muffler on stock exhaust? I am reading so much on this forum - I know very little about diesels. Any help would be appreciated.

 

[GAmes]

I think that the best mileage improver is a light touch on the go pedal. The old egg under the pedal thing. Even after bombing I get the same mileage, cuz I drive basically the same.

 

[Boldt's Wagon]

Your profile says you have a 98 12 valve, 4x4, automatic, and 4. 11 rear end. The first things I would suggest are removing/gutting the cat, adjusting the valves, replacing the fuel filter, and replacing the rear end lubricant with a synthetic. Removing or replacing the muffler depends on your individual exhaust sound tastes.



After you have run several tanks of fuel and can determine your milage you will have an indication if the timing is OK or should be checked. I believe the spec timing for your rig is 14 degrees, many people advance the timing to the 15-16 degree range. At 120,000 miles the injectors and pump overflow valve might be checked if the milage is low.

 

[Bandit1]

i got better mileage after my #5 install. i used to get 16-18 now after the plate and continued use of King oil with their NT technology lubricant i get 18-20 and i have a lead foot. (that oil is the best around my area, it is distributed by a minonite family and that is what all the diesel mechanics use around my area, it is some quality stuff

 

[Gifford]

fuel economy

The 4. 10 gearing is not helping in the fuel economy department. . You can mitgate this by installing 255-85-16 tires which are almost 35" in diameter (I think the stock 245-75-16's are 32") Other than keeping a clean air filter in it there arent many "tune up" type things you can do to a diesel. . clean oil, clean filters, light foot...

 

[WKener]

New air filter (or getting rid of the old air box and going to an open filter), gutting the catalytic converter, and replacing the muffler with a straight-through will free up your engine about as well as you can hope for. Advancing the timing (stock is usually set around 12. 5*) to 15. 5* or so like Boldt said should net you at least 1mpg more.

 

[TPCDrafting]

'98 12 valve, at least you started with a good truck!

What my plans are when the $ is there:

1. A set of guages: pyro, boost, and for you a transmission temp

2. fix the KDP (do a search you'll be reading for a year)

3. 4" exhaust (no kitty)

4. tst plate

5. injectors (most likely 370's, they're bigger and cheaper than stock oem or so I heard)

6. 4k GSK

7. oh and probably a clutch in there somewhere when the old one starts to slip.



I'm sure there's many other parts I'm missing, but this'll give you a start.